In recent years, research and development of optical coherence tomography (hereinafter occasionally abbreviated to OCT) has been underway energetically in various fields including the medical field.
An OCT technique employing a wavelength-variable light source is called swept-source OCT (abbreviated to SS-OCT). The SS-OCT technique is superior to other techniques in terms of high speed, a large signal-to-noise (S/N) ratio, and so forth and is expected to develop further.
Known wavelength-variable light sources include a vertical-cavity surface-emitting laser (abbreviated to VCSEL), which is hereinafter occasionally referred to as wavelength-variable VCSEL.
A known wavelength-variable VCSEL includes a microelectromechanical system (abbreviated to MEMS) functioning as a movable unit for varying the wavelength. The movable unit includes a mirror functioning as a component of a resonator. By displacing the movable unit with an electrostatic force, the length of the resonator is changed, whereby the wavelength of light emitted from the VCSEL is changed (NPL 1).